Brittany Thompson, a 17-year-old developmentally disabled girl who disappeared Monday, is believed to be “endangered,” say the Massachusetts State Police.

Brittany was last seen leaving the library in Medfield around 4:25 p.m. Monday, accompanied by a white man described as heavy-set with slicked-back hair and wearing a “Sons of Anarchy” T-shirt, the State Police said on its Facebook page Wednesday. The force also distributed a photo of the suspect:

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“We have reason to believe Brittany Thompson is endangered,” the message read, urging anyone with knowledge of Brittany’s disappearance to call the State Police at (508) 820-2121. Authorities did not indicate why they believe so.

Brittany, who is developmentally disabled, was last seen wearing a red sleeveless shirt, blue jeans and flip flops. She has braces, typically wears sunglasses on her head and is described as being about 5-feet 6-inches tall and weighing 140 pounds.